The present invention relates generally to thin film deposition technology pertaining to magnetic storage devices and, more particularly, to a process of manufacturing ferromagnetic-insulator-ferromagnetic tunneling devices in which atomic layer deposition is used to prepare and form the insulator film.
In the manufacture of magnetic storage devices, deposition techniques for thin films of various pure and compound materials have been developed to achieve the deposition of such thin films. Recently emerging spin polarized tunneling devices in ferromagnetic-insulator-ferromagnetic (FM/I/FM) tunneling junctions indicates that this technology has applications for non-volatile magnetic memory elements or storage media.
In the manufacture of FM/I/FM materials, ferromagnetic metallic electrodes for these devices may be deposited using available Physical Vapor Deposition (PVD) processes. Although tunneling devices can be manufactured using the Physical Vapor Deposition process, a number of acute disadvantages are noted with this technique. For example, an ultra thin continuous and high quality insulating (dielectric) film, having a thickness in the range of 5-20 xc3x85, is difficult to achieve with PVD, since discontinuities result with PVD nucleation processes. Furthermore, oxidation of ferromagnetic materials at the FM/I interface may occur during reactive sputtering process from energetic and atomic oxygen and such oxidation is undesirable, since such oxidation at the FM/I interface may be detrimental to device performance. Given the difficulties to deposit continuous oxide films with PVD and given the unavoidable effects of substrate oxidation an alternative PVD solution has implemented sputtering evaporation or molecular beam deposition of ultrathin metal films, such as Aluminum, followed successfully by an in situ oxidation. However, this method may not, so far, produce adequate results. Accordingly, standard PVD techniques may have difficulty meeting the deposition of insulating material (I) on ferromagnetic material (FM).
In the field of chemical vapor deposition (CVD), a process known as atomic layer deposition (ALD) has emerged as a different but promising technique to extend the abilities of CVD. Generally, ALD is a process wherein conventional CVD processes are divided into single-monolayer depositions, in which each separate deposition step theoretically goes to saturation at a single molecular or atomic monolayer thickness and self-terminates when the mono layer formation occurs on the surface of a material. Generally, in the standard CVD process the precursors are fed simultaneously into a reactor. In an ALD process the precursors are introduced into the reactor separately at different steps. Typically the precursors are introduced separately by alternating the flow of the precursor to combine with a carrier gas being introduced into the reactor while coexistence of the precursors in the reactor is maintained by appropriately purging the reactor in between successive introduction of precursors.
For example, when ALD is used to deposit a thin film layer on a material layer, such as a semiconductor substrate, saturating at a single molecular or atomic monolayer of thickness results in a formation of a pure desired film and eliminates the extra atoms that comprise the molecular precursors (or ligands). By the use of alternating precursors, ALD allows for single layer growth per cycle so that much tighter thickness controls can be exercised to deposit an ultra thin film. Additionally, ALD films may be grown with continuity with thickness that is as thin as a monolayer (3-5 Angstroms). This capability is one unmatched characteristic of ALD films that makes them superior candidates for applications that require ultrathin films such as insulator in FM/I/FM devices.
The present invention is directed to providing an ultra thin insulation (dielectric) layer above a ferromagnetic layer by the utilization of atomic layer deposition. Such technique may then be employed to fabricate FM/I/FM tunneling junctions, which may then fabricate magnetic storage devices. Sharp interfaces at the FM/I junctions are considered to be important characteristic for ultimate performance of FM/I/FM tunneling junction devices. Accordingly, integration of ferromagnetic bottom electrode with the insulator is an important aspect of obtaining a good FM/I junction to construct FM/I/FM devices. Current PVD technology implements a sequence of PVD depositions at high and ultra high vacuum as the leading approach for making the interface between the bottom ferromagnetic electrode and the overlying insulator material. PVD alone makes the fabrication of the insulator layer above the ferromagnetic bottom electrode elusive, but especially for an insulator which is oxide and contamination free.
Furthermore, an integration of PVD and CVD based technology is difficult to achieve considering that the difference between the vacuum range of metal PVD (which is at High Vacuum to Ultra High Vacuum) and CVD makes the PVD-CVD integration difficult or impractical. This is especially true in particular with PVD of metals and CVD of insulators. That is, depositing a bottom electrode using PVD and depositing a subsequent overlying layer of a dielectric material using CVD is difficult. Specifically, integration of high vacuum/ultra high vacuum PVD process for the deposition of the ferromagnetic layer and subsequent CVD deposition of a dielectric layer to obtain an ultrathin insulator is a challenge.
In addition, in many instances the bottom electrode of the FM/I/FM needed to be patterned. Patterning the electrode requires a process flow with multiple steps involving photolithography and etch. These steps are bound to contaminate and oxidize the top of FM electrode and subsequently deteriorate the performance of the final device. Therefore, a process flow that may provide means to protect the electrode during pattern delineation is highly desired.
A method and apparatus to deposit a first ferromagnetic metal layer onto an underlying material and to deposit a protective sacrificial layer above the first ferromagnetic layer without exposing the first ferromagnetic layer to ambient environment. Then the ferromagnetic electrode film may be patterned, if necessary. Then, the material is placed into an atomic layer deposition chamber. The protective sacrificial layer is removed in situ to expose the ferromagnetic layer and without exposing the exposed ferromagnetic layer to the ambient environment, a dielectric layer is deposited over the first ferromagnetic layer by atomic layer deposition.